Cerebrovascular accident, a disease commonly known as "stroke" remains a leading cause of death and probably constitutes the single largest category of long term disability in this country. In spite of current medical knowledge and available treatments, a major central nervous system vascular occlusion is attended by irreversible damage to the affected brain region(s). A "completed stroke" is manifest by a fixed and permanent neurological deficit. Millions of dollars have been expended in stroke research and care by Federal and private agencies without a single substantial gain in our present chemotherapeutic abilities for a completed stroke. On a clinical level, once vascular flow in any portion of the central nervous system has ceased for longer than a few minutes, a permanent "stroke" invariably follows. Accordingly, a long felt need exists to prevent permanent damage and/or reverse neurologic deficits resulting from interrupted vascular flow.
Over the years, many experiments have been conducted with materials possessing high oxygen-dissolving properties, many of which have been incorporated as constituents in "artificial blood". The concept of utilizing materials possessing high oxygen-dissolving properties for the maintenance of tissue respiration was first reported by Rodnight in 1954. See Rodnight, R.; Biochemistry Journal, Vol. 57, pg. 661. Rodnight capitalized upon the considerable oxygen solubility found in silicone oils, and sustained tissue slices by incubation in these oxygen laden oils. Approximately 12 years later, Clark reported experiments involving the total immersion of small animals in silicone oils and fluorocarbon liquids. Rats totally immersed in oxygenated silicone oil survived for one hour with no apparent ill effects, but died several hours after removal, from unknown causes. Similar experiments using synthetic fluorocarbon liquids, which dissolve about 3 times more oxygen than do the silicone oils, were performed with some success. Under these conditions, animals survived immersion in oxygenated synthetic fluorocarbon liquids and thereafter returned to apparent health. See Clark, L. C. Jr. and Gollon, F.: Science, Vol. 152, pg. 1755, (1966); and Gollon, F., Clark, L. C. Jr.,: Alabama Journal of Medical Science, Vol. 4, Pg. 336, (1967). While arterial oxygenation was reported as excellent for Clark's studies in rats, coincident impairment of carbon dioxide elimination was also reported, as was pulmonary damage from breathing flourocarbon liquids. One rat, which was observed for five days following liquid breathing, was described as being in respiratory distress and as succumbing within 15 minutes after the sub-cutaneous administration of hydrocortisone (50 mg), with copious loss of body fluid from the trachea. In this regard, Clark concluded:
These organic liquids should prove to be of value in studies of gas exchange in living tissues in animals. Organic liquids, since they can support respiration with oxygen at atmospheric pressure and have other unique qualities, may find use in submarine escape, undersea oxygen support facilities, and medical application. The pulmonary damage caused by the breathing of the organic liquids available at the present time remains a major complication of their use in man. Science, Vol. 152, pg. 1756.
Following these observations, fluorocarbon liquids were used as an incubation medium for isolated rat hearts. See Gollon and Clark, The Physiologist, Vol. 9, Pg. 191, (1966). In this work, myocardial oxygen requirements were apparently well met, however these hearts did not flourish without intermittent fluorocarbon removal and washing with oxygenated, diluted blood. This phenomen has been explained in terms of aqueous phase lack in pure fluorocarbons such that necessary ionic exchange is impeded.
More recently, considerable attention has been directed to the use of fluorocarbons as constituents of artificial blood. Sloviter, in order to overcome the problem of aqueous-metabolite fluorocarbon insolubility, made an emulsion with fluorocarbon and albumin. Sloviter's emulsion sustained the isolated rat brain by a vascular perfusion as well as did an erythrocyte suspension. See Sloviter, H. A. and Kamimoto, T.: Nature (London), Vol. 216, Pg. 458, (1967). A better emulsion was later developed comprising a detergent, "Pluronic F 68" (manufactured by the Wyandotte Chemical Corp., Wyandotte, Mich.), and fluorocarbon liquids which were properly emulsified using sonic energy. This improved emulsion permitted the replacement of most of the blood of a rat which was then reported as surviving in an atmosphere of oxygen for five to six hours. See Geyer, R. P.: Federation Proceedings, Vol. 29 No. 5, September-October, 1970; and Geyer, R. P.: Med u Ernohn, Vol. 11, Pg. 256, (1970).
Experiments have also been reported wherein fluorocarbons have been used to perfuse livers. Ten hours after in vitro fluorocarbon perfusion, the isolated liver ATP; AMP; lactate/pyruvate ratio; and a number of other metabolites were found to be as good or better than livers perfused in vitro with whole blood. See Krone, W., Huttner, W. B., Kampf, S. C., et al.: Biochemika et Biophysica Acta, Vol. 372, Pgs. 55-71, (1974). These detailed metabolic studies indicated that the organs perfused with 100% fluorocarbon liquid were redeemed "intact"; while only 75% of the whole blood infused organs maintained a similar degree of metabolic integrity. The ability of fluorocarbon perfusion to maintain cellular integrity was confirmed by electron-microscopy studies. The cells had normal mitochrondrial ultra structure after ten hours of fluorocarbon support, indicating the persistence of normal or adequate aerobic metabolism.
Fluorocarbons have also been used in experiments involving cerebral blood circulation. In Rosenblum's studies, mouse hematocrits were reduced to 10-15 by exchanging the animal's blood with a fluorocarbon solution. When the animals were respired with 100% oxygen after intravascular fluorocarbon infusions, the brains remained metabolically sound. These organs were able to reverse rising NADH levels and EEG abnormalities induced by short period nitrogen inhalation. The EEG's of fluorocarbon treated animals could be activated by the central nervous system stimulant metrazole. By these criteria, intravascular fluorocarbon does support the cerebral microcirculation and provides functions of oxygenation, metabolism and electrical activity which are normally associated with blood transport. Please refer to Rosenblum, E. I.; "Fluorocarbon Emulsions and Cerebral Microcirculation", Federation Proceedings, Vol. 34, No. 6, Pg. 1493, (May 1975).
As reported by Kontos et al., the marked vasodilation of small cerebral surface arteries which occurs in response to acute profound hypoxemia may be locally obviated by perfusing oxygen equilibrated fluorocarbon into the space under the cranial window. See Kontos, H. A., et al., "Role of Tissue Hypoxemia in Local Regulation of Cerebral Microcirculation", American Journal of Physiology, Vol. 363, Pgs. 582-591, (1978). Kontos et al. described the effect of perfusions with fluorocarbon with 100% oxygen as resulting from increased supplies of oxygen to the neural cells and consequent partial or complete relief of hypoxia, rather than to a local increase in the oxygen tension in the immediate environment of the vascular smooth muscle of the pial arterioles. Two other potential explanations for the observed action are suggested in the Kontos et al. article.
In 1977, Doss, Kaufman and Bicher reported an experiment wherein a fluorocarbon emulsion was used to partially replace cerebrospinal fluid with the intention of evaluating its protective effect against acute anoxia. According to this experiment, systemic hypoxia was produced through one minute of 100% nitrogen inhalation. A bolus of oxygenated fluorocarbon placed in the cisterna magna immediately prior to nitrogen breathing increased regional cerebrospinal fluid O.sub.2 tension by a factor of 5. During the one minute experimental period, the fluorocarbon emulsion provided twice as much brain tissue oxygen as was found in saline injected controls. Doss et al. found the anticipated regional tissue oxygenation decline attending nitrogen inhalation to be halved by the administration of the oxygen bearing fluorocarbon emulsion.
In spite of the above described experiments, there has yet to be any reported information of a practical therapeutic approach to the treatment of ischemic tissue, and particularly human ischemic central nervous system disease.